Humidified Gas Turbine Cycles Research Articles

The Application of an Artificial Neural Network as a Baseline Model for Condition Monitoring of Innovative Humidified Micro Gas Turbine Cycles

Abstract Due to high penetration of renewables, the EU energy system is undergoing a transition from large-scale centralized generation toward small-scale distributed generation. The increasing share of intermittent renewables such as solar and wind has become the main driver for dispatchable distributed energy generation technologies to maintain the grid flexibility and stability. In this context, micro gas turbines (MGTs) with high fuel and operation flexibility could play a crucial role to guarantee the grid stability, enabling deeper penetration of the intermittent renewable energy sources. Despite this, the MGT market is still considered to be niche, and there are R&D&I challenges that need to be addressed to further promote this technology in distributed generation applications. Innovative MGT cycles based on a cycle humidification concept can be considered to obtain higher system performance. However, given the fact that MGTs are installed close to the consumption points, where they are operated by nontechnical prosumers with very limited access to maintenance services, they should also offer high availability and reliability to avoid unexpected outages and secure the supply. Therefore, intelligent monitoring systems are needed that can support nonexpert end-users to detect degradation and plan maintenance before a breakdown occurs. In this study, we investigated and developed advanced methods based on artificial neural networks (ANNs) for condition monitoring of a humidified MGT cycle under real-life operational conditions. To create a high-performing model, extensive data preprocessing has been conducted to remove data outliers and select optimum model features, which provide best results. Additionally, the model hyperparameters such as learning rate, momentum, and number of hidden nodes have been altered to achieve the most accurate predictions. The results of this study have provided a baseline ANN model capable of conducting condition monitoring of a micro humid air turbine (mHAT) system, which will be applied to additional studies in the future.

Investigation of wet ammonia combustion characteristics using LES with finite-rate chemistry

The interest in climate action and building sustainable energy system, has highlighted electricity derived fuels (eFuels) and has promoted studies considering ammonia as a eFuel for sustainable transportation and as a mean of energy storage. Ammonia combustion, however, poses several challenges due to the low reactivity and potential high NOx emissions. A promising solution is to add hydrogen and steam into the fuel/air mixture. Steam contributes to the enhancement of specific power output and efficiency in humidified gas turbine cycle, and hydrogen promotes reactivity of the eFuel and can be obtained by ammonia decomposition on-site. In the present study, wet combustion of ammonia/hydrogen blends is systematic studied using one-dimensional flame analysis and Large eddy simulation (LES) to understand the flame stabilisation and NOx formation mechanisms. When hydrogen content is low (H2%<30%vol) and Tad = 1750 K, flame speed is nearly independent while flame thickness is significantly dependent on the equivalence ratio Φ due to the steam dilution. At high hydrogen content, the reverse applies. The impact of the H2% on the emission is non-monotonic, peaking between 60%∼70% at various Φ. Rich and stoichiometric combustion benefits NO reduction at a balance of H2% and steam dilution. High fidelity LES demonstrates that the steam diluted hydrogen/ammonia blends can be stably burnt in a swirl burner in a MILD regime. The wet combustion distributes the flame at low H2% and reduces local NO emission. In rich conditions, low NO emission attributes to the activation of NO reburning progress. Compared to dry condition, low steam addition (Ω=0.1) in the reactant lifts the flame and enlarges the opening angle of the swirling flow. When flame speed is low, POD analysis shows two PVC related structures - a single and a double helix, which dominate the flow and flame dynamics. While when flame speed is high, quick combustion process damps the precessing motion.

Coupling effect of key parameters of heat recovery components on the HAT cycle performance

Humid Air Turbine (HAT) cycle that uses a water-air mixture as a working fluid has a significant advantage in the distributed generation technologies and combined heat and power. The feature of the HAT cycle is that air humidification is carried out at a variable temperature. This cycle is considered as one of the optimal humidified gas turbine cycles to achieve the energy cascade utilization. However, most studies typically use the method of a single variable to investigate the coupled process of humidification and heat recovery, which limits the further performance improvement of the HAT cycle. Herein, we study the interactions among air humidification, heat recovery and system performance to elaborate the effects of interactive variables on the HAT cycle performance. Considering the complexity of the interaction of water-air ratio, aftercooler effectiveness and recuperator effectiveness, a thorough numerical analysis was carried out from the following perspectives: the thermodynamic correlation between components and systems was investigated by controlling a single parameter; the interaction of multiple variables was performed with identical turbine inlet temperature (TIT) and pressure ratio (PR) conditions; and the coupling relationship between interactive variables with a variation of TIT and PR conditions. A thorough analysis revealed that the variables that significantly impact the HAT cycle efficiency are successively RE, W/A, and AE. The analysis of the coupling effects of interactive variables under different TITs is consistent with the above results. As the PR increases, the W/A and AE have a more significant effect on HAT cycle efficiency and the effect of RE on the HAT cycle efficiency greatly diminishes. The HAT cycle efficiency, specific work output, and heat recovery achieved 43.9%, 556 kJ/kg, 5505.33 kW, where its corresponding TIT, PR, W/A, AE, RE values are 1280 °C, 8, 1.5,0.75, 0.9, respectively. Overall, a thorough analysis of interactive variables is of great significance to fully understand the effect of heat recovery on the efficiency enhancement and specific work output improvement from the thermodynamic perspective.

Identification of coherent structures in distributed swirl-stabilized wet combustion

Towards achieving sustainable and decarbonized power, biomass to electricity is an attractive pathway. To that end, the humidified gas turbine cycle is a promising technology. Recirculated steam which contains low-grade heat can be used to replace part of the air flow. This immediately reduces power loss in the compressor and increases specific power output, benefiting higher electrical efficiency compared to dry cycles. With high steam content, wet combustion leads to the so-called flameless combustion (FC) or colorless distributed combustion (CDC) which is presently investigated using large eddy simulation and a detailed finite rate chemistry method. Further insight regarding the coherent structures is obtained. Proper orthogonal decomposition method is applied on both the velocity and the heat release field aiming to explore the in-depth dynamic of flow-flame interaction in a swirl burner. Our results are the first reporting two distinct sets of helical coherent structures. A higher frequency mode or structure at Strouhal number St ~ 0.7 is caused by the vortex shedding, and a lower frequency mode at St ~ 0.1 corresponds to the off-central motion of an intermittently occurring precessing vortex core (PVC). With high steam content (hence very distributed reaction regime), more frequent occurrence of the marginally stable PVC is observed. The wet flame local extinction is evidenced to be an important driver towards the promotion and suppression of the PVC structure. Compared to the very energetic flow-flame interaction in conventional flames, FC or CDC flames undergo less fluctuations.

Investigation of wet combustion instability due to bio-syngas fuel variability

Humidified gas turbine (HGT) is a promising technology with several advantages compared to traditional thermal power plants, such as higher electrical efficiency, lower investment costs, and lower emissions. Using steam diluted, carbon neural bio-syngas as fuel in the HGT cycle leads to distributed wet combustion, often characterised by high Karlovitz number. This kind of combustion may be unstable if a small perturbation of bio-syngas fuel composition occurs and it can lead to flame blow-off. Hence, quantifying wet bio-syngas fuel variability effects on the flame physicochemical behaviour is an important step. Using uncertainty quantification, it is found that a 0.75% perturbation of a typical wet bio-syngas composition can lead to 10% fluctuation of the flame speed, 7.5% fluctuation of the flame thickness and 2% fluctuation of flame temperature for stoichiometric combustion of steam diluted reactants at gas turbine conditions. Since near stoichiometric combustion is associated with highly steam-diluted bio-syngas to retain constant thermal efficiency of HGT, ultra-wet combustion has indeed suffered from strong combustion instability led by fuel variability. The main sensitivity study shows that hydrogen variability is responsible for the high fluctuation of flame speed while methane variability is responsible for the fluctuation of thermal efficiency and flame thickness. A high pressure (HP) burner running on a typical wet bio-syngas can suffer from a change of Karlovitz number by 20 (300% by fraction) and Reynolds number by 14,000 (10% by fraction), with potential impact on flame stability and cycle performance due to small perturbation of bio-syngas composition.

Analysis of air humidification process for humid air turbine cycle with a detailed air humidifier model

Humid Air Turbine (HAT) cycle is one of the most efficient humidified gas turbine cycle that shows the potential to be competitive with combined cycle The humidifier is the distinctive component of the HAT cycle, and the air humidification process is of significance for the overall performance. However, due to the lack of reliable mass transfer coefficient, the existing theoretical model of the humidifier cannot reflect the actual humidification process. This work focuses on a method to estimate the heat transfer coefficient for the humidification process based on experimental data. The global and local mass transfer coefficients are obtained, respectively. The results show that the segmented simulation with the local mass transfer coefficients (SL-2) is significantly better than the overall simulation with the global mass transfer coefficients (SL-1). The mass transfer coefficient (hD) distributed along the height of the humidifier is obtained. At the bottom and the top of the humidifier, the sensible heat transfer and the latent heat transfer dominates the air humidification, respectively. In the packing segment of the humidifier, the heat transfer has low effectiveness of 43%, but the exergy efficiency is 96%. At the top and bottom of the humidifier, the effectiveness of heat transfer is higher than 70%, but the exergy efficiency at the bottom of the humidifier is lower than 20%. Adopting appropriate inlet air and water temperature are the available methods to reduce the exergy loss. The thermodynamic analysis in this work can provide a basis for optimizing HAT cycle configuration and humidifier structure.

Comparative study on humidified gas turbine cycles with different air saturator designs

The urge for more energy-efficient power plant systems to relieve the energy crisis triggers the design for more advanced power cycles. The humidified gas turbine cycle is considered one of the potential choices, and the air saturator performance is critical to the energy merit of such kind of system. To understand more, the performances of humidified gas turbine cycles with two types of air saturator designs were compared in this study. Type 1 air saturator was a hybrid design which combined an indirect evaporative cooler with a Maisotsenko cycle while Type 2 was a conventional indirect evaporative cooler. Detailed heat and mass transfer analysis was taken into account in the air saturator modelling. Through system simulations, it was found that all the humidified gas turbine cycle systems offered higher system efficiencies than a simple gas turbine system with recuperator. Besides, parametric studies were conducted which highlighted the effects of system inlet air temperature, turbine inlet temperature, water injection rate, and part-load ratio on the performances of the different humidified gas turbine cycle designs. The employment of Type 1 air saturator offered 9.34% and 23.55% enhancement in the system efficiencies as compared to those using Type 2 air saturator under the design and 50% part-load ratio conditions respectively. This reinforced the benefit of applying Maisotsenko cycle to the air saturator design of humidified gas turbine cycle for the enhancement of system efficiency.

Investigation on humidified gas turbine cycles with Maisotsenko-cycle-based air saturator

The urge for more energy-efficient power plant systems triggered the design for more advanced power cycle designs. The current simple cycle gas turbine shows its advantage on cost but does not fully exploit the energy available in the flue gas. In this paper, two more efficient humidified gas turbine cycles were investigated. Type 1 was a hybrid design which combined an indirect evaporative cooler with a Maisotsenko cycle and Type 2 a conventional indirect evaporative cooler as air saturator. The simulation results indicated how the operating conditions such as pressure ratio and air flow changed with the designs. Both humidified gas turbine cycle systems offered better system efficiencies than a conventional gas turbine system with recuperator and the application of Maisotsenko cycle based air saturator could further improve the gas turbine cycle efficiency. Parametric studies were also conducted which highlighted the effects of water injection rate and part-load ratio on the comparative performances of the different humidified gas turbine cycle designs.

Waste heat recovery optimization in micro gas turbine applications using advanced humidified gas turbine cycle concepts

Introduction of water in a micro Gas Turbine (mGT) has proven to be a very effective method to recover waste heat into the cycle, since it increases the mGT electrical efficiency significantly. Different routes exist for water introduction in the mGT cycle. Classical routes, like injection of steam/preheated water or the micro Humid Air Turbine (mHAT) concept, where water is introduced in the cycle by means of a saturation tower, have shown to have high potential. However none of the previously mentioned cycles exploits the full thermodynamic potential for waste heat recovery through water introduction. More advanced humidified Gas Turbine (GT) cycles have been proposed and studied for large scale GTs. So far, none of these concepts have been applied on mGT scale, despite their high potential.In this paper, we study the impact of these different, more advanced, humidified GT cycle concepts on the mGT performance. The different selected cycles – next to the classical steam injection or injection of (preheated) liquid water in the recuperated cycle and the mHAT – were: micro Humid Air Turbine Plus (mHAT+), Advanced Humid Air Turbine (AHAT) and the REgenerative EVAPoration (REVAP®) cycle concept. The impact of these concepts on the mGT cycle performance has been studied on the Turbec T100 mGT.Simulations indicated that humidifying the air of the mGT has a significant beneficial effect on cycle performance due to the increased waste heat recovery, resulting in a higher electrical power output (at constant rotational speed) or reduced fuel consumption (at constant power output), both leading to an increased electrical efficiency. Depending on the different cycle layout used, more or less waste heat could be recovered from the exhaust gas. The REVAP® concept with feedwater preheat was identified as the optimal cycle layout within the selected options. By applying this concept to the Turbec T100, most waste heat could be recovered, achieving the highest electrical efficiency increase.

Advanced Humidified Gas Turbine Cycle Concepts Applied to Micro Gas Turbine Applications for Optimal Waste Heat Recovery

Introduction of water in a micro Gas Turbine (mGT) has proven to be a very efficient way to introduce waste heat in the cycle. The injection of preheated water/steam in the mGT cycle will increase the efficiency of the cycle significantly. Different routes exist for water injection in an mGT cycle. Classical routes, like injection of steam/preheated water or the micro Humid Air Turbine (mHAT) cycle, where water is introduced in the cycle by means of a saturation tower, have shown to have high potential, however do not fully exploit the maximal potential for waste heat recovery. More advanced humidified gas turbine cycles exist on large scale, but these concepts have not yet been applied on mGT scale. In this paper, we study the impact of these different, more advanced, humidified gas turbine cycle concepts on the mGT performance. The different selected cycles – next to the classical Steam Injected Gas Turbine (STIG), injection of (preheated) water and the mHAT – were: mHAT-plus, Advanced Humid Air Turbine (AHAT) and the Regeneration EVAPoration cycle (REVAP®). Simulations indicated that humidifying the air of the mGT has a significant beneficial effect on the cycle performance, resulting in increased electrical power output and efficiency. Depending on the different used cycle layout, more waste heat could be recovered from the exhaust gas. The REVAP® cycle with feedwater preheat was identified as the optimal cycle layout within the selected cycles. Using this concept, the stack temperature could be lowered to 53 °C, corresponding to an increase in electrical power output of 128.7 kWe with a maximal absolute efficiency increase of 6.9% compared to the dry cycle layout (100.1 kWe electrical power output and 35.1% efficiency).

Blade cooling optimisation in humid-air and steam-injected gas turbines

Humidified gas turbine cycles such as the humidified air turbine (HAT) and the steam-injected gas turbine (STIG) present exciting new prospects for industrial gas turbine technology, potentially offering greatly increased work outputs and cycle efficiencies at moderate costs. The availability of humidified air or steam in such cycles also presents new opportunities in blade and disk cooling architecture. Here, the blade cooling optimisation of a HAT cycle and a STIG cycle is considered, first by optimising the choice of coolant bleeds for a reference cycle, then by a full parametric optimisation of the cycle to consider a range of optimised designs. It was found that the coolant demand reductions which can be achieved in the HAT cycle using humidified or post-aftercooled coolant are compromised by the increase in the required compression work. Furthermore, full parametric optimisation showed that higher water flow-rates were required to prevent boiling within the system. This corresponded to higher work outputs, but lower cycle efficiencies. When optimising the choice of coolant bleeds in the STIG cycle, it was found that bleeding steam for cooling purposes reduced the steam available for power augmentation and thus compromised work output, but that this could largely be overcome by reducing the steam superheat to give useful cycle efficiency gains.

A Study of Humidified Gas Turbines for Short-Term Realization in Midsized Power Generation—Part I: Nonintercooled Cycle Analysis

Humidified Gas Turbine (HGT) cycles are a group of advanced gas turbine cycles that use water-air mixtures as the working media. In this article, three known HGT configurations are examined in the context of short-term realization for small to midsized power generation: the Steam Injected Gas Turbine, the Full-flow Evaporative Gas Turbine, and the Part-flow Evaporative Gas Turbine. The heat recovery characteristics and performance potential of these three cycles are assessed, with and without intercooling, and a preliminary economic analysis is carried out for the most promising cycles.

A Study of Humidified Gas Turbines for Short-Term Realization in Midsized Power Generation—Part II: Intercooled Cycle Analysis and Final Economic Evaluation

Humidified gas turbine (HGT) cycles are a group of advanced gas turbine cycles that use water–air mixtures as the working media. In this article, three known HGT configurations are examined in the context of short-term realization for small to mid-sized power generation: the steam injected gas turbine, the full-flow evaporative gas turbine, and the part-flow evaporative gas turbine. The heat recovery characteristics and performance potential of these three cycles are assessed, with and without intercooling, and a preliminary economic analysis is carried out for the most promising cycles.

Humidified gas turbines—a review of proposed and implemented cycles

Gas turbines with air–water mixtures as the working fluid promise high electrical efficiencies and high specific power outputs to specific investment costs below that of combined cycles. Different humidified gas turbine cycles have been proposed, for example direct water-injected cycles, steam-injected cycles and evaporative cycles with humidification towers. However, only a few of these cycles have been implemented and even fewer are available commercially. This paper comprehensively reviews the literature on research and development on humidified gas turbines and identifies the cycles with the largest potential for the future. In addition, the remaining development work required for implementing the various humidified gas turbine cycles is discussed. This paper can also be used as a reference source that summarizes the research and development activities on humidified gas turbines in the last three decades.